Compensation for servo drift in industrial robots

A control technique is proposed for performing the compensation for servo drift due to a wide range of temperature fluctuations without any overshoot of the robot end effector. The effect of servo drift on the position of the end-effector is estimated and the compensation for servo drift based on the estimation is performed. Thus, an integral action need not compensate for the whole servo drift, but only for the difference between servo drift and its estimation. Since the amount of this difference is very small compared with that of the whole servo drift, an integral with a small size of the limiter, which prevents the integral wind-up, is enough to reduce the effect of servo drift on the end effector position to null. The results of an application of the proposed control to an industrial robot are compared with those of a proportional plus derivative controller